I made a macOS/iOS tournament clock for live poker games. I just wasn't happy with the few existing applications, so built and use my own. It is client/server so other people in the tournament can connect their devices and have the clock synchronized and shown on their own device, including phones and watches. It can also run dedicated/headless on Linux. I use a command line client to integration-test the networking and synching.

I never released it because 1. it's perpetually 98% done and 2. I don't feel like offering technical support for it and dealing with people who don't like it or find bugs. I may just open source it, but then I get to be a maintainer which is an even more thankless job.